Professor Sir John Bell, Regius Professor of Medicine, University of Oxford told the House of Lords Science and Technology Select Committee, that it may allow youngsters to build up some ongoing resistance that adults do not have.

“How you respond may be due to the state of your existing immunity to coronaviruses generally,” he told peers.

“There is an interesting speculation at the moment, that suggests that many people in young or middle aged groups may have T-cells that can already see coronavirus.  It may well be able to provide some protection against this pathogen when it arrives.

“A lot of kids get seasonal coronaviruses and it’s pretty common in our population and many will have quite a strong immunity to coronaviruses generally.

“That is unproven, but there is evidence now for cross-reactivity at T-cell level at least, and that well might help dampen the effects of the virus when we get it.”

Studies have shown that by the age of four, some 70 per cent of children already have antibodies against seasonal coronavirus, which could offer important protection.

“It does raise questions about what herd immunity is in this population,” added Prof Bell. “It’s a very salient point and one that will send the modellers into a tailspin.”

Professor Adrian Hayday, Chair, Department of Immunobiology, King’s College London, Group Leader, Immunosurveillance Laboratory, Francis Crick Institute said the immune systems of young people may simply be better at reacting to new viruses.

“All adults past a certain age – 30 to 35 – eventually have no thymus so their T-cells work by looking at whether they have seen something before, whereas children are very good at seeing things that are completely unknown. 

“The issue may be that children are able to see this as something fresh.”

The scientists also said that older people may suffer from immune cell ‘senescence’ where their immune cells start to shut down but are not cleared away and replaced with a working version. Cell senescence is implicated in many diseases of ageing and may be behind the ageing process itself. 

But Prof Bell said for most people coronavirus was not a serious illness.

“The people who get severe disease and die, the vast majority are elderly people and when young people get this disease they tend not to suffer very much. 

“That might be the state of people’s immune system at different ages. 70 per cent of the people who get this are completely asymptomatic, so at one end of the spectrum this is not a bad vial disease, at the other end it’s terrible.

“The vast majority of people who get this disease don’t even know they’ve had it.”

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